It was theorized in the 1960's that tumor cells bear specific antigens (TSA) which are not present on normal cells and that the immune response to these antigens might enable an individual to reject a tumor. It was later suggested that the immune response to TSA could be increased by introducing new immunological determinants on cells. Mitchison, Transplant. Proc. 2:92-103 (1970). Such a "helper determinant", which can be a hapten, a protein, a viral coat antigen, a transplantation antigen, or a xenogenous cell antigen, could be introduced into a population of tumor cells. The cells would then be injected into an individual who would be expected to be tolerant to the growth of unmodified tumor cells. Clinically, the hope was that an immunologic reaction would occur against the helper determinants, as a consequence of which the reaction to the accompanying TSA is increased, and tumor cells which would otherwise be tolerated are destroyed. Mitchison (1970) also suggests several modes of action of the helper determinants including 1) that the unmodified cells are merely attenuated, in the sense that their growth rate is slowed down or their susceptability to immunologic attack increased; 2) that helper determinants merely provide points of attack and so enable the modified cells to be killed by an immune response not directed against TSA; 3) that the helper determinants have an adjuvant action such as binding to an antibody or promoting localization of the cells in the right part of the body for immunization, in particular, in lymph nodes.
Fujiwara et al., J. Immunol. 132:1571-1577 (1984a) showed in a murine system that tumor cells conjugated with the hapten, trinitrophenyl (TNP), could induce systemic immunity against unmodified tumor cells, provided that the animals were first sensitized to the hapten in the absence of hapten-specific suppressor T cells. Spleen cells from the treated mice completely and specifically prevented the growth of tumors in untreated recipient animals. Flood et al., J. Immunol. 138:3573-3579 (1987) showed that mice immunized with a TNP-conjugated, ultraviolet light-induced "regressor" tumor were able to reject a TNP-conjugated "progressor" tumor that was otherwise non-immunologic. Moreover, these mice were subsequently resistant to challenge with unconjugated "progressor" tumor. In another experimental system, Fujiwara et al., J. Immunol. 133:510-514 (1984b) demonstrated that mice sensitized to trinitrochlorobenzene (TNCB) after cyclophosphamide (CY pretreatment could be cured of large (10 mm) tumors by in situ haptenization of tumor cells; subsequently, these animals were specifically resistant to challenge with unconjugated tumor cells.
The common denominator of these experiments is sensitization with hapten in a milieu in which suppressor cells are not induced. Spleen cells from CY-pretreated, TNCB-sensitized mice exhibited radioresistant "amplified helper function" i.e., they specifically augmented the in vitro generation of anti-TNP cytotoxicity. Moreover, once these amplified helpers had been activated by in vitro exposure to TNP-conjugated autologous lymphocytes, they were able to augment cytotoxicity to unrelated antigens as well, including tumor antigens (Fujiwara et al., 1984b). Flood et al. (1987) showed that this amplified helper activity was mediated by T cells with the phenotype Lyt-1+, Lyt-2-, L3T4+, I-J+ and suggests that these cells were contrasuppressor cells, a new class of immunoregulatory T cell.
Immunotherapy of patients with melanoma has shown that administration of CY, either high dose (1000 mg/M.sup.2) or low dose (300 mg/M.sup.2), three days before sensitization with the primary antigen keyhole limpet hemocyanin (KLH) markedly augments the acquisition of delayed type hypersensitivity (DTH) to that antigen (Berd et al., Cancer Res. 42:4862-4866 (1982); Cancer Res. 44:1275-1280 (1984a)). Low dose CY pretreatment allows patients with metastatic melanoma to develop DTH to autologous melanoma cells in response to injection with autologous melanoma vaccine (Berd et al., Cancer Res. 46:2572-2577 (1986)). The combination of low dose CY and vaccine can produce clinically important regression of metastatic tumor (Berd et al. (1986); Cancer Invest. 6:335-347 (1988a)). CY administration results in reduction of peripheral blood lymphocyte non-specific T suppressor function (Berd et al., Cancer Res. 44:5439-5443 (1984b); Cancer Res. 47:3317-3321 (1987)), possibly by depleting CD4+, CD45R+ suppressor inducer T cells (Berd et al., Cancer Res. 48:1671-1675 (1988b)). The anti-tumor effects of this immunotherapy regimen appear to be limited by the excessively long interval between the initiation of vaccine administration and the development of DTH to the tumor cells (Berd et al., Proc. Amer. Assoc. Cancer Res. 29:408 (#1626) (1988c)). Therefore, there remains a need to increase the therapeutic efficiency of such a vaccine to make it more immunogenic.
Most tumor immunologists now agree that getting T lymphocytes, the white cells responsible for tumor immunity, into the tumor mass is a prerequisite for tumor destruction by the immune system. Consequently, a good deal of attention has been focused on what has become known as "TIL" therapy, as pioneered by Dr. Stephen Rosenberg at NCI. Dr. Rosenberg and others have extracted from human cancer metastases the few T lymphocytes that are naturally present and greatly expanded their numbers by culturing then in vitro with Interleukin-2 (IL2), a growth factor for T lymphocytes Topalian et al., J.Clin. Oncol. 6:839-853 (1988). However this therapy has not been very effective because the injected T cells are limited in their ability to "home" to the tumor cite.
The ability of high concentrations of IL2 to induce lymphocytes to become non-specifically cytotoxic killer cells has been exploited therapeutically in a number of studies (Lotze et al., J. Biol. Response 3:475-482 (1982); West et al., New Engl. J. Med. 316:898-903 (1987)). However, this approach has been limited by the severe toxicity of high dose intravenous IL2. Less attention has been given to the observation that much lower concentrations of IL2 can act as an immunological adjuvant by inducing the expansion of antigen activated T cells (Talmadge et al., Cancer Res. 47:5725-5732 (1987); Meuer et al., Lancet 1:15-18 (1989)). Therefore, there remains a need to understand and attempt to exploit the use of IL2 as an immunological adjuvant.